The present disclosure relates generally to a shielding apparatus for magnetic resonance imaging (MRI), and particularly to a radio frequency (RF) shielding apparatus that maintains a desirable RF shielding performance of the RF fields.
In an MRI magnet, an RF shield is used to de-couple the RF coil from the gradient coil and other conducting structures. A desirable RF shield prevents the RF field generated by the RF coil, often at 10 Mega-Hertz (MHz) or higher, from penetrating into the gradient coil, while maintaining a desired quality factor (Q-factor) for the RF coil, and while remaining transparent to the field generated by the gradient coil, usually less than 100 kHz (kilo-Hertz). Available RF shields may include continuous conducting sheets or circuit board arrangements.
An RF shield made from a continuous conducting sheet may result in better shielding and a higher Q-factor with the use of thicker sheet material, but suffers from an increase in eddy currents induced by the gradient coil, thereby increasing the resistive loss and heating in the gradient coil. Reducing the sheet thickness makes the RF shield more transparent to the gradient field, by minimizing the induced eddy currents at these low frequencies, but at the expense of RF coil performance. An RF shield made from multiple segmented layers of a circuit board assembly may provide effective RF shielding by providing desired conduction paths for RF eddy currents. As a result of the segmentation and dielectric AC (alternating current) coupling between layers, the low frequency eddy currents may be minimized. However, these types of shield designs often suffer from high cost and susceptibility to damage.
Accordingly, there is a need in the art for a shielding apparatus for MRI that overcomes these drawbacks.